The invention relates to process and apparatus for treating synthetic filaments with hot gas or steam to introduce random curvilinear crimp of desired degrees and at the same time to introduce yarn bundle cohesion of desired degrees in filaments of various stiffnesses and cross-sectional shapes.
A number of different bulking jet designs have been disclosed for making bulked continuous filament products as disclosed in Breen and Lauterbach U.S. Pat. No. 3,638,291. Coon U.S. Pat. No. 3,525,134, which is incorporated herein by reference, employs a jet body having a passage extending along a straight axis through which yarn passes for treatment, a pair of angularly disposed conduits into the passage for directing fluid against opposite sides of the yarn, and fluid supply means connected to the conduits, one side of the passage and conduits being defined by the inner surface of a removable cap. The passage and conduits preferably have rectangular cross sections to minimize undesirable spiral fluid flow patterns which can twist the yarn erratically and produce zones of low bulk. Devices of the two references both gave greater degrees of filament entanglement and yarn bundle cohesion than those of earlier art along with a certain bulk level.
It is known, in general, that higher degrees of bulk may usually be obtained by raising the temperature and/or pressure of the bulking fluid, and that the degree of filament entanglement usually increases with higher fluid pressure. However, entanglement may become so high that the entwined filaments constrict the yarn bundle and reduce its bulk, such reduction usually is non-uniform along the length of the yarn and is considered as poor yarn quality.
The filament stiffness and cross sectional shapes affect the degrees of bulk and entanglement. For example, filaments having trilobal cross section have low torsional rigidity which permits them to more easily acquire the random filament twist and random curvilinear crimp characteristic of jet bulked products, and the higher surface area of trilobal filaments permits the high-velocity fluid to get a better grip on them. It is, therefore, relatively easy to obtain adequate bulk and excessive entanglement in trilobal filaments, particularly in those of high modification ratio. It would be desirable to reduce the entanglement while retaining bulk.
Conversely, filaments having a rounded square cross section with voids in each corner as disclosed in Champaneria and Lindbeck U.S. Pat. No. 3,745,061, FIG. 3, have higher torsional rigidity and have relatively less surface area for the fluid to act on, resulting in lower degrees of crimp and entanglement at the same fluid pressure and temperature conditions. Not only are these filaments more difficult to entangle than trilobal, their smooth exterior shape allows more of the entanglement to pull out under the tensions encountered when the yarns are wound on a package and are tufted into carpet backing. It would be desirable to obtain adequate bulk with increased entanglement.
Despite such problems, these and other filament shapes must be bulked and entangled by fiber manufacturers wishing to offer a wide range of carpet yarn products. While it is possible to design and fabricate bulking jets which give a specifically desired combination of crimp and entanglement for each product, the cost of providing an inventory of such jets and of losing production time while they are changed would be prohibitive. A means of obtaining desired combinations of bulk and entanglement from a single jet design with a minimum of change-over time and equipment cost would be greatly desired.